STARTUP_VIRTEX

Virtex User Interface to Global Clock, Reset, and 3-State Controls

The STARTUP_VIRTEX primitive is used for Global Set/Reset, global 3-state control, and the user configuration clock. The Global Set/Reset (GSR) input, when High, sets or resets all flip-flops, all latches, and every block RAM (RAMB4) output register in the device, depending on the initialization state (S or R) of the component.

NOTE

Block RAMB4 content, LUT RAMs, delay locked loop elements (CLKDLL, CLKDLLHF, BUFGDLL), and shift register LUTs (SRL16, SRL16_1, SRL16E, SRL16E_1) are not set/reset.

Following configuration, the global 3-state control (GTS), when High - and BSCAN is not enabled and executing an EXTEST instruction - forces all the IOB outputs into high impedance mode, which isolates the device outputs from the circuit but leaves the inputs active.

Including the STARTUP symbol in a design is optional. You must include the symbol under the following conditions.

• If you intend to exert external control over global set/reset, you must connect the GSR pin to a top level port and an IBUF, as shown here.
  
  
  
  
• If you intend to exert external control over global tristate, you must connect the GTS pin to a top level port and IBUF, as shown here.
  
  
  
  
• If you wish to synchronize startup to a user clock, you must connect the user clock signal to the CLK input, as shown here. Furthermore, “user clock” must be selected in the BitGen program.
  
  

You can use location constraints to specify the pin from which GSR or GTS (or both) is accessed.